Following the miniaturization and thickness reduction of electronic devices, surface-mounted packages are finding widespread use as electronic components for the electronic devices. Examples of such electronic component packages include semiconductor packages in which an electronic component such as a semiconductor element is mounted on a substrate surface and the electronic component is sealed with a resin. More specific examples include semiconductor packages such as a BOC (Board On Chip).
The increase in the volume of information to be processed created a demand for increased integration of electronic components, such as carried semiconductor elements, in various electronic devices. Such increased integration of electronic components has been realized, for example, in a MCP (Multi Chip Package) in which a plurality of electronic components such as DRAM (Dynamic Random Access memory) or flash memories is carried in a single package. Such devices require a reduced loss during signal transmission and increased signal transmission speed in the circuits between the electronic components.
For example, printed wiring boards obtained by forming a circuit (wiring circuit) by partially removing a metal layer, such as a metal foil, disposed on the surface of a metal-clad laminate are used as substrates carrying such electronic components. Such a laminate is described, for example, in Patent Document 1.
Thus, Patent Document 1 describes a laminate including a conductive foil and an insulating layer that includes a crosslinked structural body of a predetermined structure, which is a cured product of a thermosetting resin composition, and has a permittivity of 3.1 to 20 at 1 GHz. According to Patent Document 1, an electronic component manufactured using the laminated board is a highly efficient component with a small dielectric loss.
Further, the substrates for carrying electronic components are required to have not only the increased signal transmission speed, but also other properties, such as a high heat resistance and adequate elastic modulus, and also high reliability.    Patent Document 1: Japanese Patent Application Publication No. 2004-87639